The polyamides industry uses an entire range of monomers formed from diamines and from diacids, from lactams, and especially from w-amino acids. These monomers are defined by the length of the methylene chain (—CH2)n separating two amide functions —CO—NH—. These monomers are conventionally manufactured via the chemical synthesis route using, as raw materials, C2 to C4 olefins, cycloalkanes or benzene, which are hydrocarbons derived from fossil sources. For example, C2 olefins are used to manufacture the C9 amino acid used in nonanoic acid; C4 olefins are used to manufacture hexamethylenediamine; laurolactam and caprolactam are manufactured from cycloalkanes; adipic acid, Nylon 6 and Nylon 6,6 are manufactured from benzene.
Current developments in environmental matters are leading, in the fields of energy and chemistry, to the exploitation of natural raw materials originating from a renewable source being favored. It is the reason why certain studies have been undertaken in order to industrially develop processes using fatty acids/esters as raw material for manufacturing these monomers.
Document FR 2912741 thus describes a process for the synthesis of an entire range of amino acids/esters from a natural long-chain fatty acid/ester, by subjecting the latter to a catalytic cross metathesis reaction with an unsaturated compound comprising a nitrile function, followed by hydrogenation.
Document FR 2938533 describes a process for the synthesis of ω-aminoalkanoic acids or esters thereof from natural unsaturated long-chain fatty acids, passing through an intermediate compound of w-unsaturated nitrile type, one of the variants of which implements, in the final phase, a cross metathesis of the ω-unsaturated nitrile with a compound of acrylate type.
Document FR 2941694 describes a variant of the above process, in which the intermediate compound is of the unsaturated dinitrile type.
These processes result, at the end of a step of hydrogenation of the nitrile function and of the double bond, in the manufacture of amino acids.
Finally, the object of document FR 2959742 is to improve the performance levels of processes which successively implement a cross metathesis and a hydrogenation.
In these processes, the cross metathesis reactions, generally carried out between an omega-unsaturated fatty nitrile and an acrylate, or between an omega-unsaturated fatty ester and acrylonitrile, result not only in the desired product which is a nitrile-ester, but also in products resulting from a homometathesis reaction of fatty substances, such as respectively dinitriles and diesters. By increasing the amounts of catalyst used, the reaction times and/or the ratios between the reagents, it is possible to convert these coproducts resulting from homometathesis into a nitrile-ester, but these solutions prove to be expensive and not very productive.
Furthermore, the products of the homometathesis reactions (diesters or dinitriles) are heavy, long-chain products which have limited applications, which are often unrelated to the desired industrial applications for the nitrile-esters.
There is therefore a real need to develop a process for the synthesis of an unsaturated fatty compound by cross metathesis (and in particular for the synthesis of a nitrile-ester/acid) in which the amount of coproducts resulting from the homometathesis reactions is reduced and which does not require excessive consumption of catalyst.